Quick change tooling method and apparatus

ABSTRACT

A quick change tooling method and apparatus has been devised for tube bending operations in which the bend die, clamp die and pressure die as well as mandrel and wiper die, if required, are preassembled along with a tube corresponding to the tube to be bent in that particular die assembly by releasable latches or other types of releasable connectors; and each preassembled die set as described can be removed, transported and relocated on a bending machine as a complete assembly and in exact aligned operating position without readjustment and pressure setting each time that the die set is installed. A lift mechanism is provided to facilitate lifting of each die set onto and from the bending machine as well as to automatically locate each die set in proper aligned position on the machine.

BACKGROUND AND FIELD OF INVENTION

This invention relates to tube bending apparatus, and more particularlyrelates to a novel and improved method and apparatus for quickly andaccurately changing die sets for different-sized tubing to be bent orfor different types of tube bending operations.

Tube bending operations require precise alignment between a bend die,pressure die and clamping die for each size of tube to be bent. In manycases, a wiper die is required along with a mandrel which is insertedinto the tube portion to be bent. In the standard bending operation,holders are provided on the bend die table which are movable intoengagement with the bend and clamping dies, and the pressure die isadvanced linearly as the bend die is rotated with the tube to be bentbeing securely clamped in complementary grooves therebetween to undergobending and assume the configuration of the grooves as pressure isapplied. In many tube bending operations, a mandrel must be insertedinto the tube to be bent in order to prevent wrinkling or collapse ofthe portion of the tube being bent; and in many cases, a wiper die isemployed in cooperation with the pressure die to regulate the pressureapplied to the tubing during the bending operation.

In changing the various dies for different-sized tubing, the standardpractice has been to individually remove the dies and reassemble a newdie set onto the table which is time-consuming and results inconsiderable downtime. In certain tube bending applications, it has beenproposed to be able to remove more than one component part of the dieset in one step or to provide special devices to facilitate replacementof the die set in an effort to reduce downtime and, for example,reference is made to U.S. Pat. Nos. 4,178,788 to R. T. Zollweg et al,4,355,525 to J. W. Carson, 4,967,585 to S. Grimaldo, 5,148,695 to H. S.Ellis, 5,339,670 to A. Granelli, 5,426,965 to W. G. Hopf and 5,499,521to M. E. Luikart et al. Nevertheless, to the best of our knowledge, noone has devised a one-step operation in which component dies of the tubebending apparatus can be removed from the bending table and stored inassembled form so as to retain the same precise alignment andrelationship established from the previous bending operation. In thisway, the apparatus can be remounted on the table as one unit and remainin the desired relationship so as not to require extensive set-up timein preparing for the next bending operation for that particular sizedtubing; and further wherein the die set or kit is so assembled andarranged as to facilitate automated removal and reinstallation withrespect to a standard die table as well as the ability to rapidly andaccurately locate one or more die sets at one time with respect to thebend die table.

SUMMARY OF THE INVENTION

It is therefore an object of the present invention to provide for anovel and improved quick-change tooling method and apparatus for tubebending operations.

It is another object of the present invention to provide for a novel andimproved means to preassemble die sets employed in tube bendingoperations into a unitary assembly which can be removed from andreplaced on a tube bending table in a one-step operation therebysubstantially reducing downtime between tube bending operations.

It is a further object of the present invention to provide for a noveland improved method of preassembling tube bending dies into a unitaryassembly for one-step removal and replacement of die sets into accuratealignment with the bender machine for different sized tubing anddifferent types of tube bending operations.

It is a still further object of the present invention to provide for amethod of bending different sized tubing wherein die sets for each sizedtubing are preassembled and can be automatically removed and replacedwith another die set without requiring readjustment or realignment ofthe dies in each set.

In accordance with the present invention, a preassembled die set hasbeen devised for tube bending apparatus wherein the die set is comprisedof a bend die, clamp die and pressure die adapted to be mounted on aspindle of a tube bending table, the improvement comprising first meansreleasably interconnecting the pressure die and clamp die to the benddie in predetermined, aligned relation to one another and to the benddie, and handling means for engaging the die set in order tosimultaneously lift and remove said dies comprising each die set fromthe table. Preferably, the handling means is defined by lift meansoperative to lift each die set from the table and replace with anotherdie set by lowering the other die set onto the table and locating it inprealigned relation to the table. Furthermore, each preassembled die setpreferably includes a straight or bent tube corresponding to the size oftube to be bent that remains in the die set in order to permit theconnecting means to maintain the dies of each set in aligned relation toone another. Many tube bending operations require the use of a wiper dieand mandrel and which elements may also comprise a part of eachpresassembled die set when needed.

The method of changing die sets in accordance with the present inventioncomprises the steps of interconnecting each of the die sets inprealigned relation to one another for bending a selected size of tube,mounting a selected one of the die sets on a spindle support of a tubebending machine with the pressure die and clamp die aligned with oneanother and with the bend die, positioning clamp and pressure dieholders into engagement with the one die set and releasing theconnectors from engagement with the one die set, bending one or moretubes of a selected size by inserting into facing tube grooves betweenthe clamp die, pressure die and bend die and rotating the bend die tobend the tube so inserted, and releasing the clamp and pressure dieholders and connecting the connectors to releasably interconnect thedies of the one die set followed by lifting the one die set and removingfrom the spindle support. Preferably, a tube corresponding to the sizeof tube to be bent is left in the one die set prior to removal so thatthe dies maintain their prealigned relation when stored and laterreplaced on the spindle for another tube bending operation of that sizetube.

The above and other objects of the present invention will become morereadily appreciated and understood from a consideration of the followingdetailed description of preferred and modified forms of the presentinvention when taken together with the accompanying drawings in which:

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a perspective view illustrating a conventional form of tubebending machine including a die set consisting of a bend die, clamp die,pressure die and wiper die in assembled relation to the machine with amandrel inside of a tube to be bent;

FIG. 2 is a top plan view of a preferred form of preassembled die setincluding a tube to be bent;

FIG. 3 is a longitudinal sectional view of a preferred form of mandreldisconnect for a mandrel inserted into each tube to be bent;

FIG. 4 is a top plan view of a lift mechanism for removal andreplacement of a preassembled die set in accordance with the presentinvention);

FIG. 5 is a side view in elevation of the preferred form of liftmechanism shown in FIG. 4;

FIG. 6 is a top plan view of a modified form of preassembled die set inaccordance with the present invention;

FIG. 7 is a cross-sectional view of the die set shown in FIG. 6; and

FIG. 8 is a cross-sectional view in more detail of the mounting of thewiper die arm on the spindle.

DETAILED DESCRIPTION OF PREFERRED EMBODIMENT

There is shown in FIG. 1 a conventional tube bending machine 10 having amain upper bed or table surface 12 upon which is mounted a mandrelretract cylinder 14 having a plunger 16 affixed to an end of a mandrelrod 18 for insertion of a mandrel, not shown, into a tube T. A spindle20 projects upwardly from a swing arm 21 in order to control rotationalmovement of the swing arm 21 around overhanging portion 24 of themachine. Although not shown, typically the machine 10 includes a degreeof bend adjustment which is regulated by an electronic control panel, inaccordance with the degree of bend desired. An associated clamping dieholder 26 is slidable on a way 28. Additionally, a pressure die holder30 is slidable on way 32, the clamp die holder 26 and pressure dieholder 30 being movable into and away from the dies to be described in awell-known manner. One suitable form of tube bending machine is theTBH-40, manufactured and sold by Tools For Bending, Inc. of Denver,Colo.

A preferred form of die set 11 is illustrated in FIG. 2 and is broadlycomprised of a bend die 34, a clamp die 35, pressure die 36 and wiperdie 37. Each of the dies 34 to 37 is of conventional construction. Forexample, the bend die 34 is in the form of a generally U-shaped block ofhardened tool steel or alloy steel, heat-treated and nitrided, a tubegroove 38 in its outer peripheral wall between spaced, parallel top andbottom surfaces, and a semi-circular end portion 34' as shown in FIG. 1.The clamp die 35 is in the form of a generally rectangular block havinga tube groove 39 in one side wall in facing relation to one side of thebend die, the tube groove 39 being complementary to the groove 38 in thebend die. Typically the tube grooves of the bend die 34 and clamp die 35are of generally semi-circular configuration conforming to the size andconfiguration of the tube T so that each encircles one-half of the tube.A locking screw 42 in the clamp die holder 26 serves to adjust ortighten the clamp die 35 against one side of the bend die 34 with thetube T interposed therebetween during a tube bending operation.

The bend die includes a bore dimensioned to receive the upper end of thespindle 20 and a mounting plate 21 is keyed to the lower end of thespindle 20. One or more jam nuts 23 are threaded onto the upper end ofthe spindle 20 to retain the bend die 34 securely in position. Thebottom surface of the die, as shown in FIG. 1, is recessed at 40 todefine a keyway aligned with a corresponding keyway in the upper surfaceof the mounting plate 21 for the purpose of receiving a key, not shown,when the dies are installed in a manner to be described on the bendingmachine 10. In normal practice, the clamp die 35 is individuallypositioned on the clamp die holder 26 and, with the tube T held in thebend die 34, the clamp die is advanced by the clamp die holder 26against the tube and adjusted for vertical alignment as well as forparallel contact with the entire length of the die 35 along the bend die34.

The pressure die 36 is elongated and of generally rectangularcross-section except for a tube groove 44 along one side wall in facingrelation to the bend die tube groove 38 and a wiper die tube groove 46.The pressure die 36 is aligned in end-to-end relation to the clamp dieand is advanced by the pressure die holder 30 into engagement with thetube T and adjusted for vertical alignment as well as for constantpressure with the tube T along its length.

The wiper die 37 is typically employed when a mandrel is required forthe bending operation and is of elongated configuration and of generallyrectangular cross-section but including the tube groove 46 which engagesthe tube T on the same side as the bend die 34. The wiper die 37includes an arcuate end portion 48 which is of a corresponding curvatureto the end portion 34' of the bend die 34 and is advanced as far aspossible into engagement with the bend die 34, then abutting or securedto a wiper die holder 49. The wiper die holder is affixed in aconventional manner to the table 12 of the bending machine 10 and has anupstanding leg to which the wiper die may be secured by suitablefasteners. Again, when individually used, the wiper die must be adjustedfor rake and vertical alignment.

The die set is completed by a mandrel 50 which is inserted into the tubeand attached to the leading end of the mandrel rod 18. Typically, themandrel 50 is made up of a series of balls which are free to follow thecurvature of the tube T when being bent while supporting the interiorwall surface of the tube T to prevent collapse or wrinkling. Typically,the mandrel must be inserted into the tube and adjusted lengthwise bytrial and error until the optimum point of extension through the tube isreached.

In the conventional die set as hereinbefore described, the customarypractice is to reassemble each individual die 34-37 as well as themandrel 50 in position on the bending machine and follow the necessaryadjustment procedure to establish the desired pressure on the tube to bebent as well as vertical and tangential alignment of the dies and istherefore time-consuming and results in substantial downtime. In certainbending operations, a wiper die is not required and, for example, insome bending applications it is not necessary to employ a wiper die ormandrel, for example, as disclosed in our U.S. Pat. No. 4,765,168 forMETHOD AND APPARATUS FOR BENDING TUBING. In any event, depending uponthe particular tube bending requirements, the present invention enablespreassembly of the components making up the die set so that the entiredie set can be mounted on the spindle and properly aligned in a one-stepoperation not requiring the preliminary adjustment procedures asdescribed. To this end, as shown in FIG. 2, the clamp die 35 and benddie 34 are releasably interconnected by draw latches 52 affixed to thetop surfaces of the dies 34 and 35 at longitudinally spaced intervalsacross interfacing edges of the respective members; or the edges may beinterlocked in a well-known manner. Preferably, each latch 52 includes akeeper on the top surface of the clamp die having a hooked end or return54, and a toggle-type latch member 55 affixed to the top surface of thebend die 34 with a loop-shaped end 56 which can be passed over the hookend 54 by pivoting of a toggle, member 57. The keeper 53 and latch 55are permanently affixed to the top surfaces of the respective members bysuitable fasteners, such as, screws, not shown. Correspondingly, thepressure die 36 and wiper die 37 are releasably interconnected to oneanother by latch members 52 at longitudinally spaced intervals.Preferably, the latch elements 54 include an adjusting mechanism toregulate the amount of pressure exerted by the latch in drawing the diestogether when in the closed or latched position so that fine adjustmentscan be made once the latches are permanently installed or affixed ontothe dies. In this relation, the desired amount of pressure between diesis established with an appropriate sized tube T inserted between theinterfacing or complementary tube grooves. One suitable form of drawlatch is the OJOP Latch sold by Paul Moore Company of Cincinnati, Ohio,and it will be evident that other forms of latches, clamps or bolts maybe utilized to retain the dies in their exact aligned operating positionwith respect to one another.

As further shown in FIG. 2, in establishing vertical adjustment of theclamp die 35 and pressure die 36 with respect to one another and to thebend die, a series of conventional hanger brackets are providedincluding a clamp die hanger bracket 60 located somewhat intermediatelybetween the clamp die latches 52, one side of the bracket 60 fastened tothe top surface of the clamp die and the other side overhanging theclamp die holder 26. The fasteners may take the form of verticaladjustment screws which serve to properly position the clamp die withits top surface flush with that of the bend die 34. In addition, theclamp die bracket 60 includes a half-round mounting shaft, not shown,which locates the clamp die 35 in relation to tangent of bend. In asimilar manner, hanger brackets 60' are mounted on the pressure die 36at spaced longitudinal intervals with overhanging portions of eachhanger bracket affixed to pressure die spacer bar 66, as shown inFIG. 1. Additionally, lift rings 68 are anchored at spaced intervals tothe dies 34-37 to facilitate lifting of the die set onto and from thebending machine, such as, by means of an overhead crane or a liftmechanism of the type hereinafter described and shown in FIGS. 4 and 5.

In order to insert the mandrel 50 into the tube to be bent, a mandrellocator 70 is mounted on the end of the mandrel rod 18, as shown in FIG.3, the locator 70 including a threaded counterbore 72 to receive athreaded end of the mandrel rod 18 with a lock nut 73 disposed at theentrance to the counterbore. A second counterbore 74 is oppositelydirected to the first counterbore and somewhat enlarged to receive acylindrical extension 75 of the mandrel 50. The mandrel itself isstandard and includes a series of generally ball-shaped joints 76 asillustrated in FIG. 2; and the extension 75 is releasably attached tothe locator 70 by a locking pin 78 extending transversely across thecounterbore 74 and through a transverse bore in the extension 75.Suitable O-rings 80 are disposed at opposite ends of the locking pin aswell as between the counterbore 74 and extension 75, and a lube passage81 extends centrally through the rod 18, intermediate wall of thelocator, extension 75 and mandrel 50 to permit injection of a suitablelubricant into the passages 80' leading to the outer periphery of themandrel 50. The mandrel locator 70 facilitates installation of themandrel into the tube to be bent and remains with the preassembled dieset so that all that is necessary is to insert the cylindrical extension75 into the counterbore 74 and engage locking pin 78.

Various types of lift mechanisms can be employed for installation andremoval of the die set 11 with respect to the bending machine. A liftmechanism 84 is illustrated in FIGS. 4 and 5 having an adapter frame 86and a base 87 provided with spaced openings 88 for insertion of tines Fof a standard forklift truck, not shown. An upper swivel mount 90 on theframe 86 carries a plurality of support arms 92, 93 and 94 forhorizontal swinging movement about the vertical axis of the swivel mount90. Each of the arms 92-94 carries radially spaced electromagnets 96each of which is suspended from a lift collar 98 and adjustably securedto one of the arms 92-94 by lock screws 99.

A locating key 100 is disposed at the leading end of the base 87 inorder to rapidly and accurately locate the die set to a home position onthe bending machine. The locating key 100 is inserted into the keyway 40of the bend die 34 to be placed or installed on the bending machine withthe electromagnets 96 energized and brought into engagement with the topsurfaces of the bend die 34, clamp die 35 and pressure die 36. Thesupport arms 92 and 94 are disposed at 90° from one another, and theelectromagnets 96 are adjusted along the length of the respective armsto engage spaced surface portions on the top surfaces of the dies 34 to37. The intermediate bar 93 may be employed when necessary to balanceheavy off-center die sets, and the electromagnets 96 can be energizedfrom the control panel of the forklift. The lift mechanism 84 isspecifically adaptable for use in lifting die sets without the necessityof placing lift rings 68 in the die sets, for example, as shown in FIG.2.

In order to place or install a die set onto the bending machine, thelift mechanism 84 is advanced to a position above a selected die set instorage and the support arms lowered until the electromagnets move intoengagement with the top surfaces of the dies 34-37 as described. Theelectromagnets are then energized and the die set lifted and transferredover to the bending machine with the bend die 34 aligned over thespindle 20 and the locating key 100 aligned with the keyway 40. As thedie set is lowered over the spindle, the clamp and pressure die brackets60 are lowered over their respective die holders which have beenadvanced toward the bend die 34, and the bend die 34 is secured in theusual manner to the spindle 20 by one or more jam nuts 23. The mandrel50, if required, is secured to the mandrel rod 16 in the mannerdescribed. The wiper die 37, if required, is secured to the wiper dieholder 49 for radial support. After the dies have been secured, thelatches 52 are released and the clamp die 35 and pressure die 36 areretracted to a pre-bend position following which the tube T is removed.If a mandrel was required for the particular die set selected, it willhave remained in the tube T and, as noted earlier, is secured to themandrel rod. The mandrel 50 is therefore retracted from the tube by theretract cylinder 14 and the straight or bent tube T used to help holdthe die set together as an assembly is also removed. A new tube T to bebent is inserted into the die set and the mandrel 50 inserted into a newtube T.

In the manner described, each die set or assembly is installed on thetube bending machine with all of the dies in the same exact alignment aswhen they were removed and therefore does not require the customaryindividual locating and adjustment of each of the dies. Accordingly, ina manner of minutes, the installed die set is operational and tubebending operations can be resumed. When the job is completed, somewhatthe reverse procedure is followed in the removal of the die set from thebending machine. Again, a bent or straight tube corresponding to thesize of tube T to be bent by the particular die set is left in place,the latches 52 connected and the clamp die and pressure die holders 26and 30, respectively, are released. Assuming that no lift rings 68 areprovided, the lift mechanism 84 is advanced into position over the dieset and the arms 92 and 94 lowered into engagement with the top surfacesof the dies. The lift collars on the arms 92 and 94 are suitablyadjusted to place their electromagnets 96 at appropriate positionscorresponding to the location of the lift rings 68 as shown in FIG. 2,and the electromagnets are energized to lift the die set after removalof the jamb nut(s) 23 from the spindle 20. The arms 92 and 94 are thenraised to lift the die set off of the bending machine table and the arms92-94 are rotated 90° and the new tooling set lowered in place on thebender as previously described. The removed die set is transferred backto storage for the next production run.

Another form of die set is illustrated in FIGS. 6 to 8 which is of atype primarily designed for large-radius tube bending. In this form, acircular bend die 110 is mounted on a spindle 112, and the bend dieincludes a circular tube groove 114 and a clamp insert 116 provided witha tube groove 117 which extends tangentially of the tube groove 114. Aclamp die 120 and pressure die 122 are disposed alongside the bend die110 such that the clamp die tube groove 123 and pressure die tube groove124 are aligned in facing relation to the bend die tube groove 114 aswell as the insert tube groove 117. The wiper die 126 having a tubegroove 127 forms a tangential extension of the insert 116. The tubegrooves 123 to 124 are also aligned with one another along a commontangent, and a tube T' is inserted between the facing tube grooves 123,124 and 117, 127.

The wiper die 126 is joined to the bend die 110 by a wiper die arm 128,the arm 128 being in the form of a flat plate provided with an openingat its forward end to receive an upper end of the spindle 112. The wiperdie arm 128 extends rearwardly beyond the rear edge of the spindle 112,and an L-shaped crossbar 130 is attached to the rearward end of the arm128. The crossbar 130 extends transversely from the arm 128 toward thewiper die 126 and has a vertical leg 132 joined to the wiper die 126 byfasteners 134 through slotted openings 135 into one side of the wiperdie 126. The upper horizontal leg 136 of the crossbar 130 is secured tothe wiper die arm 128 by fasteners 138 extending through slottedopenings 139 of the leg.

The wiper die 126 is of the same type as shown in FIG. 2, it beingunderstood that different types of wiper dies can be used, such as,wiper die tips, round-back wipers or self-sustaining tip wiper dies. Theclamp insert 117 and wiper die 126 are releasably interconnected to aclamp die 120 and pressure die 122, respectively, by draw latches 52'which correspond to the latches 52 shown in FIG. 2 but are shown in thereleased position in FIG. 6 after the die set has been installed on thespindle 112. FIG. 6 also illustrates the mounting and disposition ofhanger brackets 60' between the top surfaces of the clamp die 120 andclamp die holder 26' as well as between the pressure die 122 and spacerbar 140 which is interposed in a well-known manner between the pressuredie 122 and pressure die holder 30.

FIGS. 7 and 8 illustrate in somewhat more detail mounting of the die setof FIG. 6 on the spindle 112, the spindle including a generallysleeve-like adapter 142 extending upwardly from the lower threaded end143 of the spindle to upper threaded end 144. The upper end of theadapter 142 is externally threaded to receive a jam nut 145 to securelyaffix the wiper die arm 128 on the top surface of the bend die 110 withcompression bearings 147 and 148 therebetween. A spindle jam nut 150 issecurely made up on the threaded end 144 to fix the adapter 142 alongwith the wiper arm 128 and bend die 110 securely in position withrespect to the spindle 112.

It will be apparent from the foregoing that stacked tool sets having twoor more families of dies of any size or shape can be removed,transferred and relocated on the bender as a complete assembly with eachdie securely locked in a required bending position to produce anacceptable bent part. Although latches have been described forinterconnecting the die sets, it will be apparent that other types ofreleasable interconnecting elements may be employed, such as, clamps orbolts in retaining the dies in exact aligned operating position withrespect to one another. If desired, suitable load cells, not shown maybe located behind the clamp and pressure dies, as well as the wiper die,if used, that indicate the optimum force required to produce anacceptable bent part. Bend data records of the necessary forces forspecific bent parts facilitate accurate, quick clamp and pressure diepressure settings. The types of dies sets herein set forth and describedspecifically in relation to FIGS. 1, 2 and 7 to 9 are given more for thepurpose of illustration and not limitation and are merely representativeof various types of die set assemblies that can be utilized inaccordance with the present invention.

It is therefore to be understood that while preferred and modified formsof invention are herein set forth and described, various modificationsand changes may be made therein without departing from the spirit andscope of the present invention as appended by the appended claims.

We claim:
 1. In tube bending apparatus wherein a die set comprised of abend die, clamp die and pressure die is mounted on a spindle of a tubebending table, the combination therewith comprising:first meansreleasably inter-connecting said pressure die and clamp die to said benddie in predetermined, aligned relation to one another and to said benddie; and handling means for releasably engaging said die set in order tosimultaneously lift and remove said die set from said table.
 2. In tubebending apparatus according to claim 1, wherein said handling means isfurther operative to mount another of said die sets on said table, saidhandling means including locator means to automatically locate saidanother of said die sets in prealigned relation to said table.
 3. Intube bending apparatus according to claim 1, wherein said die setincludes a generally cylindrical member corresponding to a tube size tobe bent, said cylindrical member being inserted between facing tubegrooves on said clamp die and said pressure die and a tube groove onsaid bending die in order to permit said first means to maintain thedies of each said die set in aligned relation to one another.
 4. In tubebending apparatus according to claim 1, wherein said die set includes agenerally tubular member corresponding to a tube size to be bent, and amandrel inserted into said tubular member in order to permit said firstmeans to maintain the dies of each said die set in aligned relation toone another.
 5. In tube bending apparatus according to claim 1, whereinsaid die set includes a wiper die, and second means connecting saidwiper die to said bend die.
 6. In tube bending apparatus wherein aplurality of preassembled die sets are provided, each of said die setsincluding a bend die, clamp die and pressure die mounted on a spindle ofa bending machine table for bending a preselected size of tube, theimprovement comprising:latch means releasably interconnecting saidpressure die and clamp die to said bend die in aligned, predeterminedrelation to one another; and lift means for releasably engaging said dieset whereby to simultaneously lift and remove said dies of each said dieset from said table and replacing with another die set.
 7. In tubebending apparatus according to claim 6 wherein each said die setincludes a tube corresponding to the size of a tube to be bent insertedbetween facing tube grooves of said clamp die and said pressure die onone side and said bend die on a diametrically opposed side of said tubein order to permit said first means to maintain the dies of each saiddie set in aligned relation to one another.
 8. In tube bending apparatusaccording to claim 6 wherein said lift means includes locator means toautomatically locate said other die set in prealigned relation to saidtable.
 9. In tube bending apparatus according to claim 6 wherein saidlatch means includes a plurality of latch members at spaced horizontalintervals between top surfaces of said clamp die and said bend die andbetween said pressure die and said wiper die.
 10. In tube bendingapparatus according to claim 6 wherein hanger brackets are mounted onsaid clamp die and said pressure die, and lift rings are mounted on atop surface of each said die set.
 11. In tube bending apparatusaccording to claim 7 wherein each said die set includes a mandrelinserted into said tube and a wiper die connected to said bend die. 12.In tube bending apparatus according to claim 11 wherein a wiper die armreleasably interconnects said wiper die to said spindle.
 13. In tubebending apparatus according to claim 11 wherein a wiper die holder isinterconnected between said table and said wiper die.
 14. In tubebending apparatus according to claim 8 wherein said lift means includesspaced, horizontally extending support arms, and electromagnetic memberson each of said support arms.
 15. In tube bending apparatus according toclaim 14 wherein said lift means is operative to lower said support armsinto engagement with a top surface of said die set and to lift said dieset by magnetic attraction.
 16. The method of changing die sets for atube bending machine wherein each of a plurality of die sets iscomprised of a bend die, clamp die and pressure die, the stepscomprising:(a) mounting each said die set on a spindle support of saidmachine with said pressure die and said clamp die aligned with oneanother and with said bend die; (b) releasably interconnecting said diesof each of said die sets with connectors extending between top surfacesof said dies in prealigned relation to one another for bending aselected size of tube; (c) positioning clamp and pressure die holdersinto engagement with each said die set and releasing said connectorsfrom engagement with each said die set; (d) bending one or more tubes ofsaid selected size by inserting each said tube in succession into eachsaid die set; and (e) releasing said clamp and pressure die holders andconnecting said connectors to releasably interconnect said dies of eachsaid die set followed by lifting each said die set and removing fromsaid spindle support.
 17. The method according to claim 16 including thefurther step of replacing each said die set with another die set andrepeating the sequence of steps (a) through (e) above.
 18. The methodaccording to claim 16 wherein one of said tubes remains inserted betweensaid dies of each said die set when lifted and removed from said spindlesupport in order to permit said connectors to maintain the dies of eachsaid die set in aligned relation to one another.
 19. The methodaccording to claim 16 wherein each of said die sets includes a wiper dieconnected to said bend die and further including the step of releasablyinterconnecting said pressure die to said wiper die.
 20. The methodaccording to claim 16 wherein step (e) is characterized byelectromagnetically lifting and lowering each of said die sets.
 21. Themethod according to claim 18 including the step of inserting a mandrelinto each said tube of said die set when said die set is mounted on saidspindle support.